docs: def fit(self, data, debug=False):
          """
          Fit each of the models in the group.
  
          Parameters
          ----------
          data : pandas.DataFrame
              Must have a column with the same name as `segmentation_col`.
          debug : bool
              If set to true (default false) will pass the debug parameter
              to model estimation.
  
          Returns
          -------
          fits : dict of statsmodels.regression.linear_model.OLSResults
              Keys are the segment names.
  
          """
          with log_start_finish(
                  'fitting models in group {}'.format(self.name), logger):
              return {name: self.models[name].fit(df, debug=debug)
                      for name, df in self._iter_groups(data)}